1. Field of the Invention
The present invention relates to a data transmission circuit which is used in a testing for memory devices, wherein the data transmission circuit alternatively outputs two different signals to an electrical terminal of the memory device.
2. Prior Art
FIG. 7 is a circuit diagram of a conventional data transmission circuit. In this Figure, the data transmission circuit consists of n data selecting circuits 22 which selectively output different pattern data from data a, b, c, . . . m, to each of n testing pins Pa, Pb, . . . , Pn, respectively. Each of the input testing pattern data a, b, c, . . . , m has a different characteristic. Pattern data signals S1a, S1b . . . , S1m from a pattern generating circuit (not shown) are latched by a flip-flop FF1 according to a real time clock signal S3. Output signals S4a, S4b . . . , S4m are supplied to each of the data selecting circuits 22. Each data selecting circuit 22 selects an output signal from the output signals S4a, S4b . . . , S4m, and generates pattern data signals S6a, S6b . . . , S6n for each of the testing pins, respectively. A data selecting circuit 22 is provided for each testing pin, and it is possible to independently select pattern data for each testing pin.
Each of the data selecting circuits 22 consists of a data selector 3 and register 6 as shown FIG. 8. The data selector 3 selects one pattern data from the pattern data a, b, c, . . . , m which are designated by the output signals S4a, S4b . . . , S4m, and outputs a pattern data signal S6 as the selected pattern data. The data selector 3 receives an output signal S13, as a selecting signal, from the register 6. The register 6 sets the selecting signal by latching a pattern data selecting signal S9 according to a register set clock signal S7.
However, the conventional data transmission circuit selects only one pattern data for one testing pin during a test execution. As a result, it is not possible to supply two different pattern data for the same testing pin. The operation of the test is therefore more complex and it requires more testing time.